The present invention relates to light weight tires.
A tire is defined as a "continuous solid or pneumatic rubber cushion encircling a wheel," p. 1237, Webster's Ninth New Collegiate Dictionary,.COPYRGT. 1989 by Merriam-Webster Inc. A tire is made from rubber, fabric, chemicals, and metal (steel). See Tires, pp. 834-861, of Vol. 16 of the Encyclopedia of Polymer Science and Engineering, .COPYRGT. 1989 by John Wiley & Sons, Inc. A pneumatic tire is a toroidal, high performance polymer composite which includes an external rubber-and-fabric covering. In these tires there are reinforcing cords which provide stability and resistance to bruises, fatigue and heat.
In bias-ply tires, the reinforcing cords extend diagonally across the tire from bead-to-bead. Layers of reinforcing cords are applied at an opposing angle of 30 to 70 degrees to balance the tire strength symmetrically across the tread-center line.
A radial tire is a pneumatic tire in which the plies of the reinforcing cords or filaments in the casing run in a radial direction (from bead-to-bead) at a 60 to 90 degree bias or crown angle in relation to the centerline of the tread (which is also the axis of rotation). Steel belts are used in radial tires in order to constrain the 90 degree carcass plies. The belt rigidity is essential to the functioning of the tire. Without it, a radial ply casing would be unstable. In addition to the steel belts, polyester cords and/or steel cords are used in the foundation structure or "carcass" (the carcass is that part of the tire between the liner and the tread) of the tire to reinforce the performance of the tire as a pressure container.
When steel reinforcement is used in construction of tires, the driving performance of the tires improves; however, the weight of the tires increases due to the weight of the steel. The extra weight of the steel reinforced tires means that vehicles that use steel reinforced tires have an increased "rolling resistance" which leads to an increase in fuel consumption. It is a desirable goal to decrease the amount of fuel consumption in all vehicles for efficiency, cost and environmental reasons.
It has been tried previously to substitute high performance organic fibers for steel in tires; however, these known organic fibers, such as p-aramid fibers, are not used in large quantities for this use because of performance problems. These performance problems include: a lack of sufficient tensile properties in the fibers such that in order to get an equivalent performance from a tire using organic fibers instead of steel, so much of the organic fiber has to be used that the weight of the tire is comparable to the weight the tire had when steel was used. Also, it has been found that the abrasion resistance and fatigue resistance of tires made with known organic fibers is not adequate for these tires to perform to desired levels.
It is desirable to produce tires that have equivalent performance to tires made with steel, but that weigh measurably less than do tires made with steel.